Hydrotreating is a type of hydroprocessing commonly used in many modern refineries, in which hydrogen is contacted in the presence of a catalyst with a hydrocarbonaceous feedstock to remove impurities, including oxygen, nitrogen, sulfur, and to saturate hydrocarbons. A frequently employed form of hydrotreating is hydrodesulfurization, which is used primarily to reduce the sulfur content from refinery intermediate streams. Hydrodesulfurization is typically used in combination with processes including feed pretreatment of catalytic reformers, fluidized-bed catalytic crackers, and hydrocrackers, and may also be used independently as a product quality improvement step for naphtha, diesel, jet, heating oil and residues, saturation of olefins, and polycyclic aromatics. Hydrocracking is another type of hydroprocessing commonly used in many modern refineries, in which hydrogen is contacted in the presence of a catalyst with a hydrocarbonaceous feedstock to produce lighter products (i.e., the average molecular weight decreases). There are numerous hydroprocessing configurations and processes known in the art, and continuous efforts to reduce energy consumption and capital cost, while improving product quality, has led to integration of hydrotreating and hydrocracking reactors in various processes.
For example, in one integration concept, a hydrotreater is combined with a hydrocracker as disclosed in U.S. Pat. No. 3,328,290 to Hengstebeck that describes a two-stage hydrocracking process wherein fresh feedstock is combined with effluent from the hydrocracking stage and the combined streams are then introduced into a hydrotreating stage. A higher-boiling fraction is then separated from the hydrotreater effluent and fractionated to produce a light product and a heavier bottoms stream, which is then recycled with hydrogen-containing gas back to the hydrocracking stage.
Another example U.S. Pat. No. 6,235,190 to Bertram describes an integrated hydrotreating and hydrocracking process in which two hydrotreating catalysts of different activities are operated in series to provide improved product quality, wherein the effluent from a hydrotreating reactor is subjected to a hydrocracking process to convert the hydrotreated effluent to lighter products with a reduced aromatic hydrocarbon content. In a further example, U.S. Pat. No. 6,261,441 to Gentry et al., a combined hydrotreating/hydrocracking process is described in which a hydrocracking stage is followed by a hydrodewaxing stage with a single feedstock and a bottoms fraction recycle to produce a naphtha product, a distillate boiling above the naphtha range, and a lubricant product.
In yet another system, as described in U.S. Pat. No. 6,328,879 to Kalnes, two independent feedstocks are hydrocracked in a catalytic hydrocracking process that employs a hydrocracking zone, a hydrotreating zone, and a high pressure product stripper to produce various products, wherein the products have a lower boiling point range than the feedstocks.
Alternatively, more than one hydrotreater reactor, and or catalyst beds may be employed for catalytic hydrogenation as described in U.S. Pat. No. 3,537,981 to Parker, or U.S. Pat. No. 6,103,105 to Cooper. While Parker's process employs a first hydrotreating reactor coupled to a separator that is in series with a second hydrotreating reactor, Cooper et al. employ two serially connected hydrotreating catalyst beds without the use of a separator. However, both Coopers and Parkers hydrotreating configurations are typically limited to only a single feedstock.
Thus, although many integrated processes have provided at least some advantage over other known configurations and methods, all or almost all of the known configurations and methods are limited to processes in which hydrocracking is the objective, or in which hydrotreating of a single boiling range (e.g., naphtha, diesel, gasoil, resid) feedstock is considered. Consequently, all or almost all of the known hydrotreating processes require separate plants where more than one feedstock is employed. Therefore, there is still a need to provide improved configurations and methods for hydrotreating of petroleum products.